Medical device having an impulse force-resistant component

ABSTRACT

A vibrator including a housing, a transducer mounted in the housing such that there is a gap between the housing and transducer; and an impulse force damper that substantially fills the gap. Such a damper includes: a first layer in contact with the housing; and a second layer in contact with the transducer and the first layer; wherein substantially no adhesion is exhibited between the first and second layers or between at least one of the first and second layers and at least one of the housing and the transducer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/910,227, filed on Nov. 29, 2013, naming Wim Bervoetsas an inventor, the contents of that application being incorporatedherein in its entirety.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates generally to medical devices, and moreparticularly, to medical devices having an impulse-force-resistantcomponent.

2. Related Art

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and/or sensorineural. Conductive hearing lossoccurs when the normal mechanical pathways of the outer and/or middleear are impeded, for example, by damage to the ossicular chain or earcanal. Sensorineural hearing loss occurs when there is damage to theinner ear, or to the nerve pathways from the inner ear to the brain.

Individuals suffering from conductive hearing loss typically receive anauditory prosthesis that provides acoustic stimulation, e.g., a hearingaid. Typically, a hearing aid is positioned in the ear canal or on theouter ear to amplify received sound. This amplified sound is deliveredto the cochlea through the normal middle ear mechanisms resulting in theincreased perception of sound by the recipient.

Individuals who suffer from conductive hearing loss typically have someform of residual hearing because the cochlea hair cells are oftenundamaged. As a result, individuals suffering from conductive hearingloss might receive an auditory prosthesis that provides mechanicalstimulation to cause a hearing percept. Such prostheses include, forexample, bone conduction devices and middle ear implants.

Auditory prostheses such as bone conduction devices function byconverting a received sound signal into a mechanical vibrationrepresentative of the received sound. An electromechanical transducercan be used for such conversion. The vibrations are delivered or appliedto the skull (cranium, mandible or teeth), and travel through the bonestructure of the skull. This skull vibration results in relative motionof the cochlea and cochlea fluid or perilymph, thereby stimulating thecochlea hair cells to cause a hearing percept.

SUMMARY

In one aspect of the disclosed technology, a vibrator is described. Thevibrator comprises: a housing; a transducer positioned within thehousing such that there is a gap between the transducer and housing; andan impulse force damper, disposed in the gap between the housing and thetransducer, configured to mechanically isolate the transducer and thehousing from each other, and to minimize impulse forces applied to thetransducer.

In another aspect of the disclosed technology, a method for making animpulse-force-resistant vibrator is described. The method comprises:providing a vibrator including a transducer mounted in a housing suchthat a gap exists between the transducer and the housing; forming afirst layer on a portion of one of the housing and the transducer; andsubstantially filling the gap between the first layer and the other ofthe housing and the transducer with a second layer; and whereinsubstantially no adhesion is exhibited between the second layer and oneof the housing and the transducer.

In a third aspect of the disclosed technology, a method of damping animpulse force to which a vibrator for an auditory prosthesis issusceptible, the vibrator including a housing, a transducer mounted inthe housing and a multilayer damper disposed between the housing and thetransducer, is described. The method comprises: compressing the damperin response to the impulse force, the compressing including: deformingat least one layer of the damper so as to dissipate energy of theimpulse force; and slipping of at least one layer with respect to one ofthe housing and the transducer, due to there being substantially noadhesion between the at least one layer between and one of the housingand the transducer. The damper comprises at least one layer thatprovides a lack of adhesion between itself and one of the housing andthe transducer in order to achieve the slipping.

In another exemplary embodiment, there is a method of making animpulse-force-resistant vibrator, the method comprising providing avibrator including a transducer mounted in a housing such that a gapexists between the transducer and the housing, forming a first layer ona portion of one of the housing and the transducer, and substantiallyfilling the gap between the first layer and the other of the housing andthe transducer with a second layer, and wherein substantially noadhesion is exhibited between, the first and second layers, or at leastone of the first and second layers and at least one of the housing andtransducer.

In another exemplary embodiment of any one or more of the methodsdetailed above or below, the forming includes coating the portion of oneof the housing and the transducer with an elastomer substantiallyconforming to manufacturing tolerances of the surface of the one of thehousing and the transducer, and the substantially filling includesinjecting an uncured or semi-cured elastic material into the gap via atleast one of one or more openings or more ducts in a mass component ofthe transducer. In another exemplary embodiment of any one or more ofthe methods detailed above or below, the method(s) further includecuring the elastic material. In another exemplary embodiment of any oneor more of the methods detailed above or below, the forming includesdepositing the first layer onto the portion of one of the housing andthe transducer so as to thereby substantially conform to manufacturingtolerances thereof, and the substantially filling includes flowing thesecond layer so as to thereby substantially conform to manufacturingtolerances of the other of the housing and the transducer.

In another exemplary embodiment of any one or more of the methodsdetailed above or below, the forming of the first layer and thesubstantially filling the gap with the second layer impose substantiallyno static preload on the transducer. In another exemplary embodiment ofany one or more of the methods detailed above or below, the vibrator isconfigured for incorporation in a bone conduction device.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present technology are best understood fromthe following detailed description when read in conjunction with theaccompanying drawings. The accompanying drawings, which are incorporatedherein and form part of the specification, illustrate exemplaryembodiments of the present disclosure and, together with thedescription, serve to explain principles, aspects and features of thepresent disclosure, and further serve to enable a person skilled in therelevant art to make and use the present technology. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Commonnumerical references represent like features/elements. Embodiments ofthe present technology are described below with reference to theattached drawings, in which:

FIG. 1A is a perspective view of an exemplary auditory prosthesis,namely a percutaneous bone conduction device, in which embodiments ofthe present technology may be implemented;

FIG. 1B is a perspective view of an exemplary auditory prosthesis,namely a transcutaneous bone conduction device, in which embodiments ofthe present technology may be implemented;

FIG. 1C is a schematic diagram illustrating an exemplary activetranscutaneous bone conduction device in which embodiments of thepresent technology may be implemented;

FIG. 2A is a schematic cross-sectional simplified view of an exemplaryvibrator that may be implemented in the auditory prostheses of FIGS.1A-1C;

FIG. 2B is a schematic cross-sectional simplified view of an exemplaryvibrator having an impulse force damper that may be implemented in theauditory prostheses of FIGS. 1A-1C;

FIG. 3A is a schematic side view of a vibrator having impulse forcedampers and dual counter-masses, in accordance with exemplaryembodiments of the present technology;

FIG. 3B depicts a vibrator having various multi-layer arrangements ofimpulse force dampers, in accordance with embodiments of the presenttechnology;

FIG. 3C depicts a vibrator having various multi-layer arrangements ofimpulse force dampers, in accordance with embodiments of the presenttechnology;

FIG. 3D depicts a vibrator having various multi-layer arrangements ofimpulse force dampers, in accordance with embodiments of the presenttechnology;

FIG. 4 is a graph illustrating the effects of using impulse forcedampers in a auditory prostheses, in accordance with embodiments of thepresent technology; and

FIG. 5 is a flowchart depicting steps by which animpulse-force-resistant vibrator can be made, in accordance withembodiments of the present technology.

DETAILED DESCRIPTION

Embodiments of the present technology are generally directed to amedical device having an impact force-resistant component. In someembodiments, the component is a vibrator. The component has a housing inwhich a functional element is disposed. There is a gap between thehousing and functional element, and the functional element may have somefreedom of movement inside the housing. An impulse force damper isdisposed in, and in at least some exemplary embodiments, fills, the gapbetween the functional element and the housing so as to substantiallyabsorb impulse forces thereby minimizing potential damage to thefunctional element Impulse forces may be created, for example, by rapidacceleration or deceleration of the component and/or by physical contactof the functional element with the component housing. Impulse forces canbe generated by external sources, such as, for example, an impulse forceapplied to an external surface of the housing of the medical device oran impulse force applied to the recipient's head. Impulse forces canalso originate from internal sources, such as, for example, movement ofthe functional component within the housing, or inertia of a moveableportion of the functional component. In those applications in which,when operating, the functional element translates, rotates, changesdimensions, or otherwise moves, the impulse force damper substantiallymechanically isolates the functional element from the housing nor doesit load the functional element so as to minimize changes in theperformance of the functional element due to the presence of the impulseforce damper.

In specific disclosed embodiments, the impulse force damper includes twolayers of material: an isolation layer adjacent the functional elementor housing, and a force dissipation layer disposed between the isolationlayer and the other of the functional element or housing. The isolationlayer minimizes adhesion of the force dissipation layer to the adjacentelement or housing on the opposing side of the isolation layer. Thisprevents the housing from altering the physical movement of thefunctional element during its operation. The isolation layer preventsthe housing from altering the physical movement functional elementduring operation. In other words, the isolation layer mechanicallyisolates the housing from the functional element so that they do notbecome one element due to their respective connections to the impulseforce damper. The force dissipation layer absorbs an impulse force bydeforming to absorb the energy in the functional element as it travelstoward the housing. For example, in some embodiments the forcedissipation layer is elastic. As such, deformation of this layer resultsin a change in the dimensions of the layer to accommodate the closinggap between the functional element and housing. That is, the forcedissipation layer deforms such that a portion of the force dissipationlayer moves to/from other regions of the gap or to/from the gap as thedimensions of the gap change.

In some disclosed embodiments, the medical device is an auditoryprosthesis, such as a bone conduction device or a middle ear implant,both of which convert received sound signals into mechanical vibrationalforces for delivery to a recipient of the prosthesis. One component ofsuch auditory prostheses is commonly referred to as a vibrator. Disposedin the housing of the vibrator are a variety of functional elements oneof which is a transducer. The transducer may be any transducer now orlater developed, such as an electro-acoustic transducer or anelectro-mechanical transducer. In some embodiments, the transducercomprises a piezoelectric element. The transducer typically alsoincludes one or more mass components, and a coupling configured toattach the vibrator to another component or the recipient. Movement ofthe piezoelectric element induces the mass components to vibrate, whichin turn generates mechanical forces. The coupling transfers mechanicalforces generated by the transducer to the recipient.

In certain embodiments, the impulse force damper includes a dampinglayer that absorbs impulse forces and an isolation layer that createsslip between itself and one of the housing or the transducer. In someembodiments, the isolation layer comprises silicone (i.e., a siliconelayer). The isolation layer allows slip between itself and one of thehousing or transducer, depending on the position of the isolation layer,so as to mechanically isolate the transducer from the housing. In somedisclosed embodiments, the impulse force damper provides isolationbetween the housing and transducer including a piezoelectric element soas to protect the piezoelectric element against impulse forces whilemaintaining the transducer output. In exemplary embodiments, the impulseforce damper protects the piezoelectric element against external andinternal impulse forces without altering a frequency response of thetransducer. According to these embodiments, the impulse force damperdoes not affect the output curve or resonance frequencies of thetransducer.

Vibrators and auditory prostheses having impulse force dampers inaccordance with certain embodiments of the present technology may havethe utilitarian feature, in at least some embodiments, of deliveringinitial resonance frequency location, or a resonance frequency locationsubstantially the same as the initial resonance frequency location, andoutput force levels (OFLs) of the designed configurations without beingadversely influenced by impulse shock forces. Some embodiments of theimpulse force damper protects the transducer from impulse forces withoutsubstantially altering the transfer function of the transducer.

As noted above, bone conduction devices have been found suitable totreat a variety of types of hearing loss and may be suitable forindividuals who cannot derive sufficient benefit from other types ofauditory prostheses. FIGS. 1A and 1B are perspective views of boneconduction devices 100 in which embodiments of the present technologymay be implemented. FIG. 1C is a schematic diagram illustrating anactive transcutaneous bone conduction device 100C in which embodimentsof the disclosed technology may be implemented. As shown in FIGS. 1A and1B, the recipient has an outer ear 101, a middle ear 102 and an innerear 103.

In a fully functional human hearing anatomy, outer ear 101 comprises anauricle 105 and an ear canal 106. A sound wave or acoustic pressure 107is collected by auricle 105 and channeled into and through ear canal106. Disposed across the distal end of ear canal 106 is a tympanicmembrane 104 which vibrates in response to acoustic wave 107. Thisvibration is coupled to oval window 110 through three bones of middleear 102, collectively referred to as the ossicles 111 and comprising themalleus 112, the incus 113 and the stapes 114. Bones 112, 113 and 114 ofmiddle ear 102 serve to filter and amplify acoustic wave 107, causingoval window 110 to articulate, or vibrate. Such vibration sets up wavesof fluid motion within cochlea 115. Such fluid motion, in turn,activates tiny hair cells (not shown) that line the inside of cochlea115. Activation of the hair cells causes appropriate nerve impulses tobe transferred through the spiral ganglion cells and auditory nerve 116to the brain (not shown), where they are perceived as sound.

FIG. 1A also illustrates the positioning of a bone conduction device100A relative to outer ear 101, middle ear 102 and inner ear 103 of arecipient of the device. As shown, exemplary bone conduction device 100Ais a percutaneous bone conduction device positioned behind outer ear 101of the recipient. In the embodiment illustrated in FIG. 1A, boneconduction device 100A comprises a vibrator 125 and a sound inputelement 126 positioned in, on or coupled to vibrator 125. Sound inputelement 126 is configured to receive sound signals and may comprise, forexample, a microphone, telecoil, etc. Sound input element 126 may alsobe a component that receives an electronic signal indicative of sound,such as, for example, from an external audio device. Typically, vibrator125 comprises a sound processor, a transducer, and various otherelectronic circuits/components. Sound signals received by sound inputelement 126 are converted to electrical signals which are processed bythe sound processor to generate drive signals which cause the actuatorto vibrate.

Bone conduction device 100A further includes a vibratory coupling 160that extends from the housing of vibrator 125 to releasably connect to apercutaneous abutment fixed to the recipient's skull bone 136. Forexample, with reference to the embodiment shown in FIG. 1A, coupling 160may be connected to a percutaneous abutment implanted under the skin 132of the recipient, within muscle tissue 134 and/or fat tissue 128. In thespecific embodiment of FIG. 1A, coupling 160 can be attached to ananchor system implanted in the recipient. Such an anchor system cancomprise a percutaneous abutment fixed to the recipient's skull bone136. The abutment can extend from bone 136 through muscle 134, fat 128and skin 132 so that coupling 160 may be attached thereto. Such apercutaneous abutment provides an attachment location for coupling 160that facilitates efficient transmission of mechanical vibrational forcesgenerated by percutaneous bone conduction device 100A.

FIG. 1B is a perspective view of another bone conduction device 100B inwhich embodiments of the present technology may be implemented. Boneconduction device 100B is a transcutaneous bone conduction devicecomprising external and implantable components. Bone conduction device100B includes a vibrator 125 and a sound input element 126 to receivesound signals. In exemplary embodiments, sound input element 126 islocated, for example, on or in vibrator 125, or it may be subcutaneouslyimplanted in the recipient.

In the arrangement illustrated in FIG. 1B, bone conduction device 100Bis a passive transcutaneous bone conduction device due to all activecomponents being external to the recipient. In such an arrangement,vibrator 125 is located behind outer ear 101, and the vibrations aretranscutaneously transferred to the skull via a pair of magnetic plates149, 150. External magnetic plate 149 is connected to vibrator 125 viacoupling 160. During normal operations, external magnetic plate 149vibrates with the actuator. Such vibrations are transcutaneouslytransferred to internal magnetic plate 150 which is magnetically coupledto external magnetic plate 149. The vibrations are transferred to skull136 via bone fixture 162.

It is to be appreciated that transcutaneous bone conduction device 100Bmay be an active transcutaneous bone conduction device in which at leastone active component is implanted in the recipient. In one sucharrangement, a signal receiver and/or various other electroniccircuits/devices are implantable. An example of such an activetranscutaneous bone conduction device is described below with referenceto FIG. 1C. It is also to be appreciated that embodiments of the presenttechnology may be implemented with other types of auditory prosthesesincluding implantable middle-ear mechanical stimulation devices (notshown). Typically, implantable middle-ear mechanical stimulation devicesare implantable within middle ear 102 and are configured to delivermechanical forces to ossicles 111 or cochlea 115. Such mechanical forcesdirectly or indirectly cause fluid motion in the cochlea which, in turn,cause the generation of nerve impulses which travel through the spiralganglion cells and auditory nerve 116 to the brain (not shown), wherethey are perceived as sound.

FIG. 1C depicts an exemplary embodiment of a transcutaneous boneconduction device 100C according to another embodiment of the presenttechnology that includes an external device 140 and an implantablecomponent 151. The transcutaneous bone conduction device 100C of FIG. 1Cis an active transcutaneous bone conduction device in that the vibratingactuator 152 is located in the implantable component 151. Specifically,a vibratory element in the form of vibrating actuator 152 is located inhousing 154 of the implantable component 151. In exemplary embodiments,much like vibrators 300A-D described below with respect to FIGS. 3A-3D,the vibrating actuator 152 is a device that converts electrical signalsinto vibration.

External component 140 includes a sound input element 126 that convertssound into electrical signals. Specifically, the transcutaneous boneconduction device 100C provides these electrical signals to vibratingactuator 152, or to a sound processor (not shown) that processes theelectrical signals, and then provides those processed signals to theimplantable component 151 through the skin 132 of the recipient via amagnetic inductance link. In this regard, a transmitter coil 142 of theexternal component 140 transmits these signals to implanted receivercoil 156 located in housing 158 of the implantable component 151.Components (not shown) in the housing 158, such as, for example, asignal generator or an implanted sound processor, then generateelectrical signals to be delivered to vibrating actuator 152 viaelectrical lead assembly 161. The vibrating actuator 152 converts theelectrical signals into vibrations.

The vibrating actuator 152 is mechanically coupled to the housing 154.Housing 154 and vibrating actuator 152 collectively form a vibratingelement. The housing 154 is substantially rigidly attached to bonefixture 164. In this regard, housing 154 includes through hole 162 thatis contoured to the outer contours of the bone fixture 164. Housingscrew 146 is used to secure housing 154 to bone fixture 164. Theportions of housing screw 146 that interface with the bone fixture 164substantially correspond to the abutment screw detailed below, thuspermitting housing screw 146 to readily fit into an existing bonefixture used in a percutaneous bone conduction device (or an existingpassive bone conduction device such as that detailed above). In anexemplary embodiment, housing screw 146 is configured so that the sametools and procedures that are used to install and/or remove an abutmentscrew from bone fixture 164 can be used to install and/or remove housingscrew 146 from the bone fixture 164.

FIG. 2A is a simplified block diagram of an exemplary auditoryprosthesis vibrator 200 representing, for example, vibrators 125described above with reference to FIGS. 1A and 1B and vibrating actuator152 described above with reference to FIG. 1C. Vibrator 200 (orvibrating element, “vibrator” herein) includes a housing 208, avibrating transducer 202 (“transducer” herein, sometimes referred to asa transducer module), a coupling apparatus 160 that is mechanicallyconnected to vibrating transducer 202 and extends from housing 208.Transducer 202 and coupling apparatus 160 are suspended in housing 208by flat spring 204. In an exemplary embodiment, flat spring 204 isconnected to coupling apparatus 160, and transducer 202 is supported bycoupling apparatus 160. The configuration of the opposing distal end ofcoupling apparatus 160 varies depending on whether vibrator 202 is acomponent of an active transcutaneous bone conduction device, such asthe devices shown in FIGS. 3A-3D, or passive transcutaneous boneconduction device.

As shown in FIG. 2A, there is void, space or gap (“gap” 206 herein)between transducer 202 and housing 208 resulting from the suspension oftransducer 202 by flat spring 204 inside housing 208. At times vibrator200 may be subjected to a sudden increase or decrease in velocityresulting from, for example, a shock or blow to the component and/or tothe recipient. When this occurs, transducer 202 may experience rapidacceleration or deceleration and/or may contact interior surface 214 ofhousing 208 with a force referred to herein as an impulse force. Such animpulse force may be sufficient to damage the transducer. Due to theconfiguration of vibrator 200, impulse forces which are more likely tocause damage to transducer 202 are those forces which have a vectorcomponent that is parallel to vibration axis 210 since transducer 202 isprovided freedom of movement along axis 210. That is, an impulse forcemay be applied to top surface 212 of transducer 202 when transducer 202travels through gap 206 to, perhaps, strike housing interior surface214. FIG. 2B depicts the same simplified block diagram of auditoryprosthesis vibrator 200 as shown in FIG. 2A. However, in FIG. 2B,vibrator 200 includes an impulse force damper 216 disposed betweentransducer top surface 212 and housing interior surface 214. Impulseforce damper 216, in at least some exemplary embodiments, fills gap 206,as shown in FIG. 2B. Impulse force damper 216 does not adhere to atleast one of the adjacent transducer and housing interior surfaces 212and 214, respectively. Such mechanical isolation prevents housing 208from interfering with the operational performance of transducer 202.Impulse force damper 216 substantially absorbs impulse forces created byphysical movement of transducer 202 along vibration axis 210.

FIGS. 3A-3D are block diagrams of a vibrator 200, referred to herein asvibrators 300A-300D, respectively. Various embodiments of impulse forcedamper 216 are implemented in vibrators 300A-300D, which are describedwith reference to the bone conduction devices illustrated in FIGS.1A-1C. For brevity, only differences presented in FIGS. 3A-3D aredescribed below.

Referring to FIG. 3A, vibrator 300A has a transducer 302 comprised of apiezoelectric element 301 attached to two masses 307A, 307B, byextension arms 304A, 304B, respectively. As shown in the exemplaryembodiments of FIGS. 3A-3D, the piezoelectric element 301 can includepiezoelectric extension arms 304A and 304B (i.e., extension arms 304A,304B are piezoelectric elements and function collectively, with thepiezoelectric element 301, as a single piezoelectric element). Apiezoelectric element converts an electrical signal applied thereto intoa mechanical deformation (i.e., expansion or contraction) of thepiezoelectric element. The extent of deformation of the piezoelectricelement in response to a given applied electrical signal depends on thematerial properties of the element, the orientation of the electricfield with respect to the polarization direction of the element, thegeometry of the element, etc., as is well known in the art.

Each mass 307 is formed of material such as tungsten, tungsten alloy,brass, etc., and may have a variety of shapes. Additionally, the shape,size, configuration, orientation, etc., of each mass 307 may be selectedto optimize the transmission of the mechanical force from piezoelectrictransducer 302 to the recipient's skull and to optimize the frequencyresponse of the transducer. In certain embodiments, the size and shapeof each mass 307 is chosen to ensure that there sufficient mechanicalforce is generated and to optimize the response of the transducer 302.

In specific embodiments, masses 307 have a weight between approximately1 g and approximately 50 g. Furthermore, the material forming masses 307may have a density, e.g., between approximately 2000 kg/m3 andapproximately 22000 kg/m3. As shown, piezoelectric element 301 is alsoattached to coupling 160 which is utilized to transfer the mechanicalforce generated by the transducer to the recipient's skull.

Transducer 302 is suspended in housing 125 such that there is a gap 306between housing 308 and transducer 302. That is, housing interiorsurface 314 and the surface 312 of the masses are in spacedjuxtaposition to define a gap 306A-306D. As noted, gaps 306 allows forthe vibration of transducer 302 in vibration axis 310. In the embodimentillustrated in FIG. 3A, impulse force dampers 316A-D are disposedbetween housing interior surface 314 and the adjacent surfaces 312 ofmasses 307 to substantially fill their respective gap 306 betweenhousing interior surface 314 and juxtaposed mass surface 312. In atleast some embodiments, impulse force dampers 316 prevent the rapidacceleration and deceleration of masses 307. Such movement may cause asignificant impulse force to be applied to piezoelectric element 301given the size of masses 307 and length of extension arms 304. For easeof description, impulse force damper 316A will be described below. Withthe exceptions noted below, the description of impulse force damper 316Aapplies to impulse force dampers 316B-D.

In certain embodiments, damper 316A includes at least two layers, anelastic force dissipation layer 318A and an isolation layer 320A. Forcedissipation layer 318A substantially dissipates the kinetic energy inthe moving mass 307A thereby preventing the mass from experiencingsudden acceleration or deceleration which would cause piezoelectricelement 301 from experiencing a potentially damaging impulse force.Isolation layer 320A is disposed between force dissipation layer 318Aand transducer mass 307A. In some embodiments, isolation layer 320A isformed from a silicone elastomer. In the same or other embodiments,force dissipation layer 318A is substantially elastic shock absorbinglayer formed of a soft and elastic material such as a cured liquidsilicone rubber material. As noted, force dissipation layer 318A deformsas mass 307A travels toward the housing. This deformation absorbsenergy, causing a decrease in the rate at which the transducer travelsand limits the amount of force transmitted to the piezoelectric elementsor the mass elements. In some embodiments, frequency response and outputof vibrator 300A is maintained because housing 308 and mass 307 aredecoupled and prevented from adhering to each other. For example, asshown in the exemplary embodiment of FIG. 3A, the isolation layer 320Adisposed between the force dissipation layer 318A and the housinginterior surface 314 decouples mass 307A from housing 308 and preventsmass 307A from adhering to housing 308.

Force dissipation layer 318A is formed of material(s) configured toexhibit sufficiently low stiffness and/or sufficient elasticity so as toflex or deform in response to a compressive force caused by transducermass 307A traveling toward housing surface 314, thereby reducing therate at which gap 306A decreases. Elastic materials strain whenstretched and return to their original state relatively quickly once thestress is removed. In certain embodiments, force dissipation layer 318Ais an elastic material made from one or more of a soft silicone typematerial, a foam material, and a rubber material.

Thus, exemplary force damper 316A is configured to achieve impulse forcedissipation through a combination of deformation of an elastic materialexhibiting sufficiently low stiffness and shear damping via substantialgross slip along the interface where a surface of damper 316A abuts anadjacent layer or surface. In one embodiment, impulse force dissipationlayer 318A comprises a cured liquid silicone rubber.

Isolation layer 320A is disposed between force dissipation layer 318Aand mass 307A to prevent adhesion of the force dissipation layer to masssurface 312. Isolation layer 320A can be configured to achieve this bypreventing adhesion between itself and mass 307A. In some embodiments,the force dissipation and isolation layers are configured to exhibitsubstantially no adhesion between each other.

Impulse force damper 316A comprises a relatively thin isolation layer320A and a relatively thick impulse force dissipation layer 318A. Itshould be appreciated that the absolute and relative thicknesses offorce dissipation layer 318A and isolation layer 320A depicted in FIG.3A is for ease of illustration, and is not intended to illustratespecific or relative dimensions. In certain embodiments, isolation layer320A has a thickness between 0.1 mm and 0.6 mm and impulse force damper316A has an overall thickness of between 0.2 mm and 10 mm. Forcedissipation layer 318A can have a thickness of between 0.4 mm to 0.9 mm.Other size ranges, larger or smaller, than the exemplary size rangesdescribed herein, are possible depending on the dimensions of thevibrator and the gap. In alternative embodiments, layers 320A and 318Ahave substantially the same thickness.

In some embodiments isolation layer 320 is a relatively thin film orsheet arranged on either side of mass components 307 and impulse forcedissipation layer 318 is a relatively thicker shock absorbing/dampingmaterial arranged between isolation layer 320 and housing 125. Incertain embodiments, the isolation layer 320 can comprise a curedsilicone elastomer having a thickness of less than about 70 micrometers(μm). The force dissipation layer 318 is configured to deform laterallywith respect to a surface of the transducer (such as a surface 312 ofmass component 307) and an opposing surface 314 of housing 308 in orderto dissipate an impulse force applied to the vibrator. In embodiments,impulse force dissipation layer 318 can comprise a cured siliconerubber.

In certain embodiments, isolation layer 320A comprises a material havingone of more of the following: an American Society for Testing andMaterials (ASTM) technical standard D2240 Durometer Type A scale valueof about 50; a Tensile Strength of about 1450 psi (pounds per squareinch); an Elongation of about 1000%; a Tear Strength (Die B) of about250 ppi (pounds per inch); a Stress @200% Strain of about 300 psi; and aSpecific Gravity of about 1.16. A commercially available example of sucha material is Model No. MED 49-01 (a type of silicone elastomer)manufactured by NUSIL® Technology, LLC, in a cured state, which isavailable in sheets of about 0.002 inches thick.

In certain embodiments, impulse force dissipation layer 318A comprises amaterial having one of more of the following: an ASTM technical standardD2240 Durometer Type OO scale value less than or equal to about 40; aTensile Strength of about 325 psi; an Elongation of about 1075%; a TearStrength of about 60 ppi; a Stress @100% Strain of about 10 psi; aStress @300% Strain of about 30 psi; and a Stress @500% Strain of about65 psi. A commercially available example of such a material is Model No.MED 82-50 1 0-02 (a type of liquid silicone rubber) manufactured byNUSIL® Technology, LLC, in a cured state.

Thus, in the embodiment of FIG. 3A, force dissipation layer 318A isconfigured to exhibit non-negligible adhesion to housing surface 314 andsubstantially no adhesion to isolation layer 320A. This enables impulseforce damper 316A to dissipate energy through a combination ofdeformation and shear damping along the interface between with isolationlayer 320A. Shear damping refers to the lateral sliding or slipping ofthe layers 318A and 320A, which is possible due to lack of adhesionbetween the layers.

In certain embodiments, isolation layer 320A is configured to exhibitsubstantially no adhesion with respect to an adjacent surface of impulseforce dissipation layer 318A so as to allow gross slip via at least someshear damping along one or more of an interface between: dissipationlayer 318A and isolation layer 320A. For example, isolation layer 320Acan be configured to act as an anti-adhesive or lubricant with respectto dissipation layer 318A. Shear damping along an interface betweendissipation layer 318A and isolation layer 320A can be explained byconsidering the behavior of two adjacent surfaces that are in contactwith each other. A clamping force may exist between these two surfaces.Such a clamping force can result from externally applied loads, or froma mating or press fit that produces an interface common to the twoparts. If an additional exciting force is gradually imposed, the twoparts may initially react as a single elastic body such that there isshear on the interface, but not enough to produce relative slip at anypoint. As the force increases in magnitude to the extent that the forceconstitutes application of an impulse force, the resulting shearingtraction at some places on the interface can exceed the limiting valuepermitted by the friction characteristics of the two mating surfaces(e.g., a surface of isolation layer 320A and an adjacent surfacedissipation layer 318A). According to the embodiments described herein,isolation layer 320A of impulse force damper 316A exhibits substantiallyno adhesion to dissipation layer 318A such that the limiting value andshearing traction are sufficiently low so as to allow gross slip tooccur along the interface where dissipation layer 318A and isolationlayer 320A mate with each other. In regions where a surface of impulseforce damper 316A mates with mass component 307A, 307B or housing 308,microscopic slip of adjacent points on opposite sides of the interfacecan occur. In an alternative embodiment, there is slip between the twolayers of the impulse force damper 316A. According to this embodiment,there is slip between force dissipation layer 318A and isolation layer320A. In an exemplary embodiment, the slipped region extendssubstantially over the entire interface between layers 318A and 320A sothat gross slip can occur. In some embodiments, slip occurs betweenisolation layer 320A and one of the interior housing surface 314 or themass 307 depending on which is in contact with isolation layer 320A.Subsequent application of a tangential force can produce slip over aportion of the interface even if a peak tangential force is not greatenough to affect gross slip or sliding along the interface. In certainembodiments, isolation layer 320A can comprise a relatively thin (withrespect to layer 318A) foil, sheet, or film of silicone elastomercoating a surface of a portion of a transducer, such as a region orsurface of mass component 307. For example, isolation layer 320A can bea cured silicone elastomer applied to mass components 307 so as to allowgross slip between impulse force dissipation layer 318A and isolationlayer 320A. In some embodiments, gross slip occurs between the isolationlayer 320A and the housing 308 or mass 307, depending on which one theisolation layer 320A is in contact with. In an alternative embodiment,slip occurs between force dissipation layer 318A and the isolation layer320A.

As seen in FIGS. 3A-D, embodiments of impulse force dampers comprisevarying arrangements of layers 320 and 318 in which isolation layer 320is in contact with either housing surface 314 or transducer mass surface312, and force dissipation layer 318 is in contact with the othersurface. In certain embodiments, layers 320 and 318 are arranged andconfigured so that the layers substantially conform to manufacturingtolerances of a respective, abutting housing interior surface 314 andmass surface 312. In FIG. 3B, isolation layers 320A, 320B are applied toor interface with housing interior surfaces 314 and force dissipationlayers 318A, 318B are applied to or interface with mass surfaces 312.Impulse force dampers 316C, 316D are configured as described above withreference to FIG. 3A. In FIG. 3C, all four impulse force dampers 316A-Dare configured the same as impulse force dampers 316A, 316B of FIG. 3B.In FIG. 3D, impulse force dampers 316A-D each have two isolation layers320 applied to or interfacing with housing interior surface 314 and masssurface 312, with the respective force dissipation layer 318 disposedbetween the two isolation layers.

According to embodiments, the vibrators shown in FIGS. 3A-D can be usedin auditory prostheses, such as, but not limited to, activetranscutaneous bone conduction devices. The vibrators 300A-D can be usedfor other bone conduction devices. For example, the vibrators shown inFIGS. 3A-D with an impulse force damper 316 comprising a forcedissipation layer 318 and an isolation layer 320 can be used in othertypes of bone conduction devices in a similar manner to absorb impulseforces without substantially altering the frequency response of thevibrator. In certain embodiments such vibrators are configured forincorporation in bone conduction devices. For example, the vibratorsdescribed below with reference to FIGS. 3A-D can be implemented intranscutaneous bone conduction devices 100B and 100C, percutaneous boneconduction devices 100A, and in subcutaneous bone conduction devices.

Each layer of the exemplary impulse force dampers 316A-D are shown inFIGS. 3A-3D as having a rectangular shape. It should be understood thatthis is for ease of illustration, and that the shape of each layerdepends on the material used, the properties of that material, and themanner in which the layers are applied.

FIG. 4 is a graph illustrating the operational performance of a vibratorimplementing different embodiments of impulse force damper 216.Specifically, FIG. 4 illustrates the relationship between transduceroutput force level (OFL) 410 for a given operational frequency response420 of the transducer. Because bone conduction devices deliver sound asvibrations in skull bone 136, FIG. 4 plots OFL 410 as a measure ofvibration in relation to sound. A decibel (dB) in relation to 1micronewton (μN) is a measure of the vibrational force produced by thedevice at different frequencies 420, which are expressed in Hertz (Hz).

Waveform 430 shows the OFLs across frequency range 420 for a vibrator ofa transducer which does not implement an impulse force damper asdescribed herein. Waveform 450 shows the OFLs across frequency range 420for the same vibrator of the same transducer which implements anembodiment of the impulse force damper described herein. As shown inFIG. 4, at most frequencies 420 the OFL 410 of a vibrator implementingan impulse force damper is the same or substantially the same as the OFLof a vibrator which does not implement an impulse force damper. Thesimilarity of waveforms 430 and 450 illustrates that the impulse forcedamper does not load the transducer, and provides sufficient mechanicalisolation of the housing to prevent the housing from loading thetransducer. The similarity of waveforms 430 and 450 shows that theimpulse force damper with an isolation layer does not substantiallyaffect the frequency response of the vibrator, and that the locations ofthe respective resonance peaks 460 and 470 are almost identical. FIG. 4illustrates that the performance of the vibrator with and without theimpulse force damper with the isolation layer is substantially similar.This is achieved in part because in a quiescent state, the impulse forcedamper with the isolation layer imposes substantially no static preloadon the transducer. As shown in FIG. 4, the impulse force damper isconfigured such that it causes a substantially insignificant effect onthe frequency response of the vibrator. This is utilitarian in at leastsome embodiments because the impulse force damper helps to absorbimpulse forces without affecting performance, thus ensuring that arecipient receives the appropriate stimulation as designed.

More specifically, waveform 450 reflects a limited effect on OFL 410 atlower values of frequencies 420, including only slight damping(magnitude attenuation) and shifting of first resonance peak 460, andsubstantially no effect at higher frequencies 420, as evidenced by thelack of any amplitude change. In particular, frequency response curve450 shows that the amplitude of first resonance peak 460 is slightlydamped by about 2-3 dBs. Frequency response curve 450 also shows firstresonance peak 460 for a vibrator with an impulse force dampercomprising both layers is shifted upwards by around 100 Hz fromapproximately 700 Hz to approximately 800 Hz.

Waveform 440 shows the OFLs across frequency range 420 for a vibrator ofa transducer which implements the force dissipation layer of the impulseforce damper, and not the isolation layer. As shown in FIG. 4, waveform440 is offset from waveform 430, resulting in the OFL of a vibratorimplementing just the force dissipation layer being different than theOFL of a vibrator without an impulse force damper, at least for asubstantial portion of frequency range 420. This altering of the OFL atcertain frequencies is due to the load placed on the transducer by thehousing due to the reduced mechanical isolation which would otherwise beprovided by the absent isolation layer. The additional loading occursbecause the housing and mass effectively become a single element due tocontact with the dissipation layer, and move as a unitary mass. Thisadded mass of the housing on the transducer significantly alters theperformance of the transducer. This altered performance of thetransducer is undesirable as it results in inappropriate stimulationsignals being delivered to the recipient, which can have the undesirableeffects of altering output quality or preventing a hearing percept frombeing generated.

With continued reference to FIG. 4, frequency response curve 440 of avibrator having an impulse force damper as described herein, and lackingan isolation layer can exhibit a relatively large effect on OFL 410. Asshown the first peak 460 of such a vibrator can be damped significantly(e.g., by more than 10 dBs) and can be shifted upwards or downwards byas much as +−2000 Hz. Such a large shift of first resonance peak 460 maycause a vibrator to exhibit harmonic distortion in excess of 400 Hz,making the vibrator unsuitable for incorporation into auditoryprosthesis.

While various impulse force damper configurations and arrangements mayadequately protect a vibratory actuator/transducer from shock forces,configurations affecting OFL 410 enough to shift resonance peaks 460 or470 to different frequencies 420 may not be suitable for use intransducers for auditory prostheses. Relative to a quiescent state inwhich no damper is mounted vis-à-vis the transducer, a damper can bedescribed as applying a preload to a transducer if the mounted damperhas the effect of applying a static force (a bias force) to thetransducer, however small the preload might be. For example, a layer ofdamping material injected in its uncured state into a gap between a mass(attached to a transducer) and the housing so as to fill the mightpreload the transducer if the damping material expands when ittransitions into its cured state. As another example, a vibrator relyingsolely upon a mechanical element such as spring to dampen impulse forcesmay preload a transducer or a mass component to the extent that OFL 410is unduly affected. Impulse force dampers that have a minimal, limitedeffect on a transducer's OFL 410 while also dissipating impulse forcesso as to substantially isolate a transducer from the impulse force aremore suitable for auditory prostheses such as bone conduction devicesImpulse force dampers configured to dissipate an impulse force viadeformation thereof thereby preventing damage to transducer while alsohaving minimal shifting or damping effects on resonance peaks 460 and470 are suitable impulse-force-resistant transducers for incorporationin an auditory prosthesis. In contrast, impulse force dampers applyingsufficient preload to a transducer or mass component affects OFL 410 interms of the amplitudes of resonance peaks 460 or 470 being alteredand/or resonance peaks 460 or 470 being shifted to different frequencies420. Such alterations and shifts can make such impulse force dampersless desirable for use in bone conduction devices.

FIG. 5 is a flowchart depicting steps by which animpulse-force-resistant vibrator can be made. The flowchart depicted inFIG. 5 is described with reference to the embodiments described above.However, FIG. 5 is not limited to those example embodiments. The stepsof methods for making impulse-force-resistant vibrator do notnecessarily have to occur in the order shown in FIG. 5 and describedbelow. According to embodiments, some of the steps shown in FIG. 5 areoptional. Optional steps are indicated in the flowchart by dashed lines(see, e.g., steps 504, 506, and 514).

The method begins in step 502 when a vibrator including a transducerwith preassembled mass components is provided. After the vibrator isprovided, the method optionally proceeds to step 504 where the massesare connected to a vibratory actuator of the transducer, oralternatively to step 506 when no mass components are to be included. Inoptional step 504, one or more mass components are attached to avibratory actuator. In certain embodiments this step comprises attachinga piezoelectric element to at least one mass component. By completingstep 504, embodiments such as those described above can be implementedwhereby the transducer comprises single or dual mass components attachedto a piezoelectric actuator. In embodiments, step 504 can compriseconnecting one or more mass components to piezoelectric elements.

After the mass components are connected to the vibratory actuator (ifdesired), the method optionally proceeds to step 506 where thetransducer is attached to a supporting member, or alternatively to step508 when the provided transducer is already attached or mounted to thesupporting member. In embodiments, optional step 506 comprises mountingthe transducer or actuator to a coupling of an anchor system such asthose described above with reference to FIGS. 1A-1C. In an embodiment,step 506 can comprise attaching the transducer structure with itspiezoelectric elements and mass components to the supporting member.After the transducer is optionally attached to a supporting member, flowproceeds to step 508. In step 508, the transducer provided in step 502is suspended or mounted within a first portion of a housing so that gapsare between the juxtaposed transducer and surfaces of the first portionof the housing. In embodiments, step 506 comprises positioning thetransducer such that there is a gap between internal surfaces of thefirst portion of the housing and the transducer. In an embodiment, step508 can comprise mounting the transducer within a bottom portion of ahousing so that gaps are between the transducer and the bottom portionof the housing.

In step 510, a first layer is formed on one of a surface of the housingand the transducer. Embodiments of this step can comprise depositing thefirst layer of the impulse force damper as an isolation layer via spray,sputter, or vapor deposition onto a region of one of the housing and thetransducer. This step forms the first layer such that it substantiallyconforms to manufacturing tolerances of the surface to which it isapplied. Embodiments such as those depicted herein can implemented by analternative implementation of step 510 that forms dual isolation layersof the damper on surfaces of the housing and the transducer. Embodimentscan include applying the first layer as a film, foil, or other suitablecoating onto target surface(s) and region(s) of the housing and/ortransducer. Regardless of the coating and application technique employedto implement step 510, the first layer substantially conforms tomanufacturing tolerances of target surface(s) and region(s). It shouldbe appreciated that step 510 may be performed prior to the assembly ofthe vibrator in the prior steps. In embodiments, step 510 comprisespositioning the isolation layer on one of an internal surface of thehousing and a surface of the mass component(s). In an alternativeembodiment, step 510 comprises positioning the force dissipation layeron one of an internal surface of the housing and a surface of the masscomponent(s). This step can comprise injecting one of the forcedissipation layer or the isolation layer through opening(s) in the masscomponent(s) onto an interior surface of the bottom portion of thehousing. In additional or alternative embodiments, step 510 can compriseforming one of the force dissipation layer or the isolation layerdirectly onto a surface the mass component(s). After the first layer isformed, flow proceeds to step 512.

In step 512, the remainder of the gap between the first layer and anopposing surface of the other of the housing or the transducer aresubstantially filled with a second layer of the impulse damper. In anembodiment, when step 510 placed the force dissipation layer on the masscomponent(s), step 512 comprises positioning the isolation layer on theforce dissipation layer. According to embodiments, step 512 can compriseinjecting a shock absorbing elastic material such as, but not limitedto, an uncured or semi-cured gel into an opening in the transducer, suchas, for example, via ducts in the mass component(s). This step cancomprise injecting one of the force dissipation layer or the isolationlayer through opening(s) in the mass component(s) into the remainder ofthe gap between an interior surface of the bottom portion of the housingand the mass component(s). For example, step 512 can comprise injectingan uncured or semi-cured elastic silicone gel into a gap correspondingto the region via opening(s) and/or duct(s) in the transducer. Incertain embodiments the openings and/or ducts have diameters ofapproximately 1.2 mm. This step can comprise flowing the second layeronto the opposing surface of the other of the housing or the transducersuch that the second layer conforms to manufacturing tolerances of thesurface. After the gap is substantially filled, flow optionally proceedsto step 514 when an uncured or semi-cured material is used.

In optional step 514, any uncured or semi-cured material used for thesecond layer in step 512 is cured as needed and then flow proceeds tostep 516. After curing in step 514, the impulse force damper exhibitssufficient elastic properties (i.e., elasticity) so as to dissipate animpulse force via deformation thereof thereby substantially isolating avibratory actuator/transducer from the impulse force.

In step 516, a second portion of housing is attached to the firstportion of the housing from step 508 and the housing is sealed. Incertain embodiments, step 516 can comprise sealing opening(s) and/orduct(s) in the transducer, such as the opening(s) or duct(s) used instep 512. After the housing is sealed, flow proceeds to step 518 wherethe method ends.

The present technology described and claimed herein is not to be limitedin scope by the specific example embodiments herein disclosed, sincethese embodiments are intended as illustrations, and not limitations, ofseveral aspects of the present technology. Any equivalent embodimentsare intended to be within the scope of the present technology. Indeed,various modifications of the present technology in addition to thoseshown and described herein will become apparent to those skilled in theart from the foregoing description. For example, the present technologyhas been described in the context of a medical device, and specificallyin the context of a moving component of an auditory prosthesis. Itshould be appreciated that the impulse force damper described herein maybe implemented in any device in which a component may be damaged due toimpulse forces. Such modifications are also intended to fall within thescope of the appended claims.

1. A vibrator comprising: a housing; a transducer positioned within thehousing such that there is a gap between the transducer and housing; andan impulse force damper, disposed in the gap between the housing and atleast a portion of the transducer, configured to mechanically isolate atleast a portion of the transducer and the housing, and to minimizeimpulse forces applied to the transducer relative to that which would bethe case in the absence of the impulse force damper.
 2. The vibrator ofclaim 1, wherein for at least one of a plurality of regions of the gapbetween the housing and the at least a portion of the transducer, theimpulse force damper fills the gap in that at least one region, andwherein said impulse force damper is configured to minimize adhesionbetween abutting surfaces of at least one of the damper/housinginterface and the damper/transducer interface.
 3. The vibrator of claim1, wherein said damper is formed of an elastic damping material.
 4. Thevibrator of claim 3, wherein, in response to a decrease in distancebetween the housing and transducer in the at least one region, theelastic damping material deforms by laterally expanding therebyincreasing dimensions of the at least one region.
 5. The vibrator ofclaim 2, wherein the damper is configured to provide at least aneffectively negligible load on the transducer relative to that whichwould be the case in the absence of the damper.
 6. The vibrator of claim1, wherein the damper has a mass that is effectively insubstantialrelative to the mass of the transducer so as to minimize an effect on anoutput response of the vibrator relative to that which would be the casein the absence of the presence of the damper.
 7. The vibrator of claim1, wherein the damper comprises: a first layer of a first material incontact with one of either the housing and the transducer; and a secondlayer of a second material in contact with the other of either thehousing and the transducer, wherein the first and second layers haveabutting surfaces defining a first layer/second layer interface.
 8. Thevibrator of claim 7, wherein the first and second materials areantifriction materials with respect to each other.
 9. The vibrator ofclaim 8, wherein one of the first and second materials is an elasticdamping material.
 10. The vibrator of claim 9, wherein the one of thefirst and second layers formed by the elastic damping material is asubstantial volume of the damper, and the other of the first and secondlayers has a negligible thickness.
 11. The vibrator of claim 10, whereinthe other of the first and second layers substantially conforms tomanufacturing and assembly tolerances in the surface of the abuttingsurface of one of the housing and transducer.
 12. A bone conductiondevice, comprising: a mass; an actuator configured to move the mass togenerate vibrations to evoke a hearing percept; and a housingencompassing the mass and the actuator, wherein a damper is located in aspace between a housing wall of the housing and the mass.
 13. The boneconduction device of claim 12, further including: an arm, wherein themass is located at a first end of the arm, and the arm is connected tothe actuator at a location away from the first end of the arm, whereinthe actuator moves the arm, thereby moving the mass.
 14. The boneconduction device of claim 12, wherein: the damper extends from the massto the wall of the housing.
 15. The bone conduction device of claim 12,wherein: the damper includes a damper material and an isolation layerthat separates the damper material from one of the mass and the housingwall.
 16. The bone conduction device of claim 12, wherein: the damper isa first damper; the bone conduction device includes a second damperlocated in a second space between another portion of the housing andanother side of the mass on an opposite side of the mass from the firstdamper.
 17. The bone conduction device of claim 12, wherein: the boneconduction device is configured such that output of the bone conductiondevice to evoke a hearing percept is at least effectively the same asthat which would be the case in the absence of the damper being presentbetween the mass and the housing wall.
 18. A method of damping animpulse force to which a vibrator for an auditory prosthesis issusceptible, the vibrator including a housing, a transducer mounted inthe housing and a multilayer damper disposed between the housing and thetransducer, the method comprising: compressing the damper in response tothe impulse force, the compressing including: deforming at least onelayer of the damper so as to dissipate energy of the impulse force; andslipping, due to there being substantially no adhesion between one ormore of: two layers of the damper with respect to each other; at leastone layer of the damper with respect to the housing; and at least onelayer of the damper with respect to the transducer.
 19. The method ofclaim 18, further comprising: imposing, in a quiescent state,substantially no static preload on the transducer by the damper.
 20. Themethod of claim 18, wherein the damper is configured to cause asubstantially insignificant effect on the frequency response of thevibrator.